The present invention relates to a tricolor video signal generator, such as a video game, usable with a monochrome picture display device, said generator comprising inter alia a circuit producing red (R), green (V) and blue (B) color signals, and a resistive matrix network deriving a luminance signal (Y) from the three above-mentioned color signals.
The invention has particularly, but not exclusively, for its object the so-called "video" games intended to be connected to a television set, either to the aerial input, or to the video input for peripheral equipment with which current television sets are equipped.
Almost all the video games which are manufactured at present are designed for use with a color television set, and their possible connection to a black-and-white television set poses a problem of contrast for the use of certain programmable games.
It is known that because of the requirements for compatibility, a picture which is transmitted encoded in color can usually be displayed on a black-and-white television set, the different color hues then being represented by luminance levels from black to purely white, including intermediate grey-values. This does not offer any disadvantage for the reception of a moving picture, which is perfectly visible in spite of the absence of the original color information.
This does not hold for certain video games where the color information constitutes a main element for recognizing certain elements in the received picture; so two very different colors may be represented by two grey-shades whose luminance values are very close to each other, and which consequently are very difficult to differentiate.
This situation may be disadvantageous for the commercial distribution of video games as the circumstances in which they can be used with a black-and-white television set are very numerous: a second television set in the house, a second house in which a black-and-white television set is installed, etc.
The same difficulty may occur with the use of certain microprocessors which usually employ a normal, commercially available television set as the display terminal, and where the interpretation of text, graphs, etc. in black and white has the same problem as regards contrast.
It is also possible to mention for a near future the case where it may be desired to connect a video game or a microprocessor to a video text receiver or an electronic telephone directory, which enlarges the field of application of these apparatus.
The French Patent Specification No. 2,417,901 describes a circuit by means of which it is possible to modify the grey scale of a monochrome picture display device, and more particularly to increase the luminance level of the signals which are too close to the black level; however, said circuit is more specifically intended for incorporation in a picture display device which renders it impossible to use it in a normal, commercially available television set; moreover it only acts on the levels close to black, such as blue, it definitely does not act on the difference between two colors whatever their position in the grey-scale and it requires combinations of comparatively complicated and costly logic and analog circuits.